Method for planarizing circuit board and method for manufacturing semiconductor device

ABSTRACT

A method for planarizing a circuit board, has a step of fixing a circuit board having wiring layers on both sides to a board having a flat surface through an adhesive layer, wherein said circuit board is pressed from above by a flat member on fixing thereof.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for planarizing acircuit board, and a method for manufacturing a semiconductor device.

[0003] 2. Description of the Related Art

[0004] Semiconductor devices contribute to the reduction in size ofinformation communication equipment, official-electronic equipment,household electronic equipment, industrial electronic equipment such asmeasuring apparatuses and assembling robots, medical electronicequipment, and electronic toys, and facilitates the miniaturizationthereof.

[0005] The manufacturing of semiconductor devices requires semiconductorelements and wiring boards for mounting them thereon. As technology formounting a semiconductor element on a wiring board, a wire bondingmethod has been the mainstream conventionally. However, a flip-chipmethod capable of reducing the mounting area of semiconductor elementshas become the mainstream in recent years. In a wiring board on which asemiconductor element is to be mounted, in mounting a semiconductorelement by a wire bonding method, the electrodes on the semiconductorelement are bonded outward to the electrodes of the wiring board placedoutside the semiconductor element by wire, respectively, and hence theelectrodes on the wiring board may be placed with a larger pitch thanthe pitch of electrodes of the semiconductor element. Contrarily, inmounting a semiconductor element with a flip-chip method, the electrodesof the semiconductor element must be located corresponding to theelectrodes of the wiring board in a one-to-one relationship. Therefore,as wiring board for mounting a semiconductor element thereon with aflip-chip method, a high-density board, i.e., a board on which a fineline is to be formed is desirable. Further, a reduction in size of asemiconductor device requires a board to which a wiring layer isconnected through an inner via.

[0006] It is a ceramic multi-layer printed circuit board to satisfy theforegoing demands. However, a ceramic plate board generally has alimitation on its cost reduction as compared with resin boards such asglass epoxy boards, which actually restricts the introduction intoconsumer-electronics products.

[0007] A resin plate board has a higher possibility that a larger costreduction can be achieved due to its manufacturing method than in thecase of a ceramic plate board. However, the resin board has a lowerrigidity than that of a ceramic plate board, and hence there occurnonuniform wiring density, and deformation when the board decreases inthickness, resulting in a difficulty in flip-chip mounting of asemiconductor element.

SUMMARY OF THE INVENTION

[0008] In view of the foregoing, it is therefore an object of thepresent invention to provide a method for manufacturing a semiconductordevice with stability.

[0009] A method for planarizing a circuit board according to the presentinvention, comprises: a step of fixing a circuit board having wiringlayers on both sides to a board having a flat surface through anadhesive layer, wherein the circuit board is pressed from above by aflat member on fixing thereof.

[0010] A method for manufacturing a semiconductor device according tothe present invention, comprises: a step of fixing a circuit boardhaving wiring layers on both sides to a board having a flat surfacethrough an adhesive layer; a step of mounting a semiconductor element sothat a plurality of electrodes on the semiconductor element areface-down bonded to the exposed wiring of the fixed circuit board in aone-to-one relationship; a step of filling the clearance between thecircuit board and the semiconductor element with an insulating resinpaste; a step of curing the insulating resin paste; and a step ofpeeling off the circuit board on which the semiconductor element ismounted from the interface with the adhesive layer on the board having aflat surface, wherein the circuit board is pressed from above by a flatmember on fixing the circuit board.

[0011] A method for manufacturing a semiconductor device according tothe present invention, comprises: a step of fixing a circuit boardhaving wiring layers on both sides to a motherboard having a flatsurface through an adhesive layer; a step of mounting a semiconductorelement so that a plurality of electrodes on the semiconductor elementare face-down bonded to the exposed wiring of the fixed circuit board ina one-to-one relationship; a step of filling the clearance between thecircuit board and the semiconductor device with an insulating resinpaste; and a step of curing the insulating resin paste, wherein thecircuit board is pressed from above by a flat member on fixing thecircuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic cross sectional view of a semiconductordevice in a first step of the manufacturing process according to a firstembodiment of the present invention;

[0013]FIG. 2 is a schematic cross sectional view of the semiconductordevice in a second step of the manufacturing process according to thefirst embodiment of the present invention;

[0014]FIG. 3 is a schematic cross sectional view of the semiconductordevice in a third step of the manufacturing process according to thefirst embodiment of the present invention;

[0015]FIG. 4 is a schematic cross sectional view of the semiconductordevice in a fourth step of the manufacturing process according to thefirst embodiment of the present invention;

[0016]FIG. 5 is a schematic cross sectional view of the semiconductordevice in a fifth step of the manufacturing process according to thefirst embodiment of the present invention;

[0017]FIG. 6 is a schematic cross sectional view of a semiconductordevice in one manufacturing process according to a third embodiment ofthe present invention;

[0018]FIG. 7 is a schematic cross sectional view of semiconductordevices in one step when a plurality of the semiconductor devices aremanufactured on one flat board; and

[0019] FIGS. 8(a) and 8(b) are schematic cross sectional views of asemiconductor device in different stages of the manufacturing processaccording to a fourth embodiment of the present invention. Descriptionof Numerals 11, 21, 31 glass plate (flat board) 41 sintered aluminaboard having openings 12, 22, 32, 42 circuit board 13, 33 adhesive sheet23, 43 adhesive layer 14, 24, 34, 44 semiconductor element 15, 25, 35,45 insulating resin (paste) 16, 27 semiconductor device 26 filler with ahigh coefficient of thermal expansion 46 opening 121 wiring layer.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Below, the present invention will now be described by way ofembodiments with reference to the drawings.

[0021] (Embodiment 1)

[0022] FIGS. 1 to 5 show a schematic cross section of a semiconductordevice each in different steps of the manufacturing process according toa first embodiment in the order presented.

[0023] A first step: a circuit board 12 having wiring layers 12 on bothsides is so constructed that the wiring layers 121 on both sides areelectrically connected through inner via, and the board material ismainly composed of epoxy resin wherein an aramid fiber is dispersed inthe epoxy resin. It is noted that glass fiber may be used in place ofthe aramid fiber. The circuit board 12 has a size of 12 mm×12 mm×0.4 mm,and the flatness in the area of 12 mm×12 mm is approximately 30 microns.Then, a glass plate 11 with a flatness of 5 microns or less is prepared.The glass plate 11 has a size of 40 mm×40 mm×1.5 mm. An adhesive sheet13 (B-EL10 manufactured by Nitto Shinko) mainly composed of epoxy resinin the semi-cured state is stacked between the circuit board 12 and theglass plate 11. The adhesive sheet 13 has a size of 13 mm×13 mm×0.04 mm.Heating to approximately 50° C. on stacking results in betterworkability.

[0024] A second step: the laminated circuit board 12, adhesive sheet 13,and glass plate 11 are applied with heat while being applied withpressure so that the circuit board 12 may become flattened to cure theadhesive sheet 13 in the semi-cured state. The conditions of thisprocess are 150° C. and 20 g/cm². It is noted that depressurization oncuring the adhesive sheet 13 enables the bonding between the circuitboard 12 and the glass plate 11 without mixing of bubbles therein. Thecircuit board 12 is well bonded to the glass plate 11 after curing ofthe adhesive sheet 13, and the flatness of the circuit board 12 is foundto be 10 microns or less. Also, the circuit board 12 is pressed fromabove with a board for press, which ensures the planarization.

[0025] A third step: a semiconductor element 14 is face-down mounted onthe planarized circuit board 12. The following mounting method isadopted. That is, a gold bump is formed on the electrode of thesemiconductor element 14, and the end of the gold bump is applied with aconductive adhesive, and the gold bump and the wiring electrode on thecircuit board 12 are bonded to each other by the conductive adhesive.The conductive adhesive is a totally in-house manufactured productcontaining silver as conductive material, and the curing temperature istaken as 120° C.

[0026] A fourth step: an insulating resin paste 15 is filled in theclearance between the semiconductor element 14 and the circuit board 12,after which the insulating resin paste 15 is cured by a heat-treatment.The insulating resin paste 15 is a totally in-house manufactured productcontaining epoxy resin as main component, and containing silicon-dioxideas filler, and the curing temperature is taken as 150° C. This resultsin a semiconductor device 16 bonded to the glass plate 11 through theadhesive sheet 13. After being cured, this insulating resin paste 15exerts a function of preventing the semiconductor device from bending.

[0027] A fifth step: in order to take off the semiconductor device 16from the glass plate 11, the cured adhesive sheet 13 is heated toapproximately 100° C. The cured adhesive sheet 13 has a glass-transitiontemperature of approximately 70° C., and hence at a temperature of 70°C. or more, the structure of the adhesive sheet 13 is softened, whichfacilitates the removal of the semiconductor device 16.

[0028] In this embodiment, a glass plate is used, however, a sinteredalumina board or SUS board may be also used as long as it has a goodflatness. Further, as board having a flatness, a motherboard can be alsoutilized. In such a case, it is not necessary to take off the circuitboard 12 and the semiconductor element 14 from the board in the finalstep, which affords a convenience that it can be used as it is. In thatprocess, it is desirable to use an anisotropic conductive adhesive asmaterial for the adhesive layer.

[0029] Also, as comparative example, the same experiment is carried out,except that an adhesive sheet and a thermoplastic adhesive sheet havinga lower adhesion force than that of the adhesive sheet used in the aboveembodiment are used. The results are shown in Table 1. TABLE 1 Materialsfor Adhesion force adhesive sheet (per area of 5 mm ø) MountabilityB-EL10 manufactured 2 kgf OK by Nitto Shinko (Embodiment 1) RevaalphaNo. 3195H 0.5 kgf   NG manufactured by Nitto Denko Double-faced tape for1 kgf NG stationery manufactured by Nitto Denko

[0030] Each adhesive sheet is measured for its adhesion force in thefollowing manner. That is, the underside of a cylindrical componenthaving a diameter of 5 mm, and made of stainless steel is fixed with theadhesive sheet. Then, the force exerted when the component made ofstainless steel is vertically pulled to be peeled off from the adhesivesheet is measured. The mountability is judged by if the connectionbetween the semiconductor element and the circuit board is achieved inthe mounting method of the semiconductor element described in theembodiment 1.

[0031] Also, in this embodiment, only one circuit board with a size of12 mm×12 mm is bonded onto the glass plate with a size of 50 mm×50 mm.However, it is needless to say that, even if a plurality of the circuitboards are bonded as shown in FIG. 7, the same results can be obtained.

[0032] Further, in this embodiment, the wiring formed on both sides ofthe circuit board is electrically connected through an inner via.However, it is needless to say that, a so-called, multi-layer printedcircuit board, in which connection is achieved through inner layers, canprovide the same results.

[0033] (Embodiment 2)

[0034] In an embodiment 2, an adhesive paste is used without using anadhesive sheet. The adhesive paste is a 3016 manufactured by Locktite,and a solvent-less type thermosetting insulating resin paste mainlycomposed of epoxy resin.

[0035] First, the adhesive paste is applied on the area of 13 mm×13 mmon a glass plate by screen printing. At this step, the film thickness isapproximately 50 microns. In this state, a heat-treatment is conductedat a temperature of approximately 50° C. to render the adhesive paste inthe semi-cured state, thereby laminating a circuit board. Then, asemiconductor device is manufactured in the same process as in theembodiment 1 to obtain the same results as in the embodiment 1.

[0036] Also, it is confirmed that when the circuit board and the glassplate are laminated without rendering the adhesive paste in thesemi-cured state, the same results are obtained.

[0037] (Embodiment 3)

[0038] The manufacturing method of a semiconductor device according to athird embodiment of the present invention will now be described based onFIG. 6. FIG. 6 shows a schematic cross section of the semiconductordevice in one manufacturing process of the third embodiment.

[0039] A circuit board 22 is bonded to a flat glass plate 21 through anadhesive layer 23, resulting in good flatness of the circuit board 22. Asemiconductor element 24 is mounted on the circuit board 22, and aninsulating resin is filled in the clearance between the semiconductorelement 24 and the circuit board 22.

[0040] The difference from the embodiment 1 is in the materialconstituents of the adhesive layer. That is, a filler 26 having a largercoefficient of thermal expansion than that of the material for theadhesive layer is contained in the adhesive layer of this embodiment.The adhesive layer used is a totally in-house manufactured product, andthe material constituents thereof are approximately 70 ppm/° C. epoxyresin and approximately 150 ppm/° C. glass bead as filler 26.

[0041] The use of the adhesive layer 23 having such materialconstituents causes the filler 26 having a high coefficient of thermalexpansion in the adhesive layer 23 to expand in the heat-treatmentconducted when a semiconductor device 27 is removed from the glass plate21. This facilitates the removal of the semiconductor device 27.

[0042] (Embodiment 4)

[0043] The manufacturing method of a semiconductor device according to afourth embodiment of the present invention will now be described basedon FIG. 8. FIG. 8 shows a schematic cross section of the semiconductordevice in the manufacturing process of the fourth embodiment.

[0044] A circuit board 42 is flat, and it is bonded to a sinteredalumina board 41 provided with openings 46 so as to each correspond toits respective electrode of the circuit board 42 through an adhesivelayer 43, resulting in a good flatness. A semiconductor element 44 ismounted on the circuit board 42 having a good flatness. The sinteredalumina board 41 has openings 46, and hence the inspection of electricalconnection between the semiconductor element 44 and the wiring layer 121of the circuit board 42 can be conducted in this state.

[0045] As a result of the inspection, when a poor connection is found,the semiconductor element 44 and the circuit board 42 have not beenbonded to each other yet. Accordingly, the semiconductor element 44 orthe circuit board 44 can be replaced with ease to repeat the processuntil connection can be obtained. With only the one in which connectionhas been achieved in this manner, an insulating resin 45 is filled inthe clearance between the semiconductor element 44 and the circuit board42 to effect bonding thereof.

[0046] As described above, the manufacturing method of the semiconductordevice of the present invention provides an effect that, with even aresin board having a bad flatness, a flip-chip mounting of asemiconductor element can be implemented with stability.

[0047] The manufacturing method of the semiconductor device of thepresent invention provides an effect that, when the adhesion force ofthe adhesive layer is 1.5 kgf/5 mmΦ or more, even with a resin boardhaving a large warp, planarization can be achieved to implement aflip-chip mounting of a semiconductor element with stability.

[0048] The manufacturing method of the semiconductor device of thepresent invention provides an effect that, when a filler is contained inthe insulating resin of the adhesive layer, and the coefficient ofthermal expansion of the filler is larger than that of the insulatingresin, the removal of the semiconductor device from the flat board canbe conducted by a heat-treatment with ease.

[0049] The manufacturing method of the semiconductor device of thepresent invention provides an effect that, when an opening is providedat a desired point of the flat board, the inspection of connectionbetween the semiconductor element and the circuit board can be carriedout, and hence defective products will not be manufactured.

What is claimed is:
 1. A method for planarizing a circuit board,comprising a step of fixing a circuit board having wiring layers on bothsides to a board having a flat surface through an adhesive layer,wherein said circuit board is pressed from above by a flat member onfixing thereof.
 2. A method for manufacturing a semiconductor device,comprising: a step of fixing a circuit board having wiring layers onboth sides to a board having a flat surface through an adhesive layer; astep of mounting a semiconductor element so that a plurality ofelectrodes on said semiconductor element are face-down bonded to theexposed wiring of said fixed circuit board in a one-to-one relationship;a step of filling the clearance between said circuit board and saidsemiconductor element with an insulating resin paste; a step of curingsaid insulating resin paste; and a step of peeling off said circuitboard on which said semiconductor element is mounted from the interfacewith said adhesive layer on said board having a flat surface, whereinsaid circuit board is pressed from above by a flat member on fixing saidcircuit board.
 3. A method for manufacturing a semiconductor device,comprising: a step of fixing a circuit board having wiring layers onboth sides to a motherboard having a flat surface through an adhesivelayer; a step of mounting a semiconductor element so that a plurality ofelectrodes on said semiconductor element are face-down bonded to theexposed wiring of said fixed circuit board in a one-to-one relationship;a step of filling the clearance between said circuit board and saidsemiconductor device with an insulating resin paste; and a step ofcuring said insulating resin paste, wherein said circuit board ispressed from above by a flat member on fixing said circuit board.
 4. Amethod for manufacturing a semiconductor device according to claim 2,wherein the adhesion force of said adhesive layer is 1.5 kgf/5 mmΦ ormore.
 5. A method for manufacturing a semiconductor device according toclaim 3, wherein the adhesion force of said adhesive layer is 1.5 kgf/5mmΦ or more.
 6. A method for manufacturing a semiconductor deviceaccording to claim 2, wherein said adhesive layer is, first, athermosetting paste, and then, bonds said circuit board and said flatboard by a heat-treatment.
 7. A method for manufacturing a semiconductordevice according to claim 3, wherein said adhesive layer is, first, athermosetting paste, and then, bonds said circuit board and said flatboard by a heat-treatment.
 8. A method for manufacturing a semiconductordevice according to claim 2, wherein said adhesive layer is, first, athermosetting resin film in the semi-cured state, and then, bonds saidcircuit board and said flat board by a heat-treatment.
 9. A method formanufacturing a semiconductor device according to claim 3, wherein saidadhesive layer is, first, a thermosetting resin film in the semi-curedstate, and then, bonds said circuit board and said flat board by aheat-treatment.
 10. A method for manufacturing a semiconductor deviceaccording to claim 2, wherein said adhesive layer has a structure inwhich a filler is contained in the material of said adhesive layer, andthe coefficient of thermal expansion of said filler is larger than thecoefficient of thermal expansion of the material for said adhesivelayer.
 11. A method for manufacturing a semiconductor device accordingto claim 2, wherein a plurality of said circuit boards are fixed to saidsingle flat board through said adhesive layer, and said semiconductorelements are mounted on a plurality of said circuit boards,respectively.
 12. A method for manufacturing a semiconductor deviceaccording to claim 3, wherein a plurality of said circuit boards arefixed to said single flat board through said adhesive layer, and saidsemiconductor elements are mounted on a plurality of said circuitboards, respectively.
 13. A method for manufacturing a semiconductordevice according to claim 2, wherein in said step of fixing said circuitboard to a board having a flat surface through said adhesive layer, saidadhesive layer is heated to 150° C. to effect curing and bondingthereof, while in said step of peeling off said circuit board on whichsaid semiconductor element is mounted from the interface with saidadhesive layer on said board having a flat surface, said adhesive layeris heated to 100° C. to be softened.
 14. A method for manufacturing asemiconductor device according to claim 2, wherein said flat board isprovided with an opening at a position corresponding to the position ofsaid electrode of said circuit board, and after mounting saidsemiconductor element, and before filling said insulating resin paste,said opening is used to carry out an inspection of connection betweensaid semiconductor element and said circuit board.
 15. A method formanufacturing a semiconductor device according to claims 3, wherein saidflat board is provided with an opening at a position corresponding tothe position of said electrode of said circuit board, and after mountingsaid semiconductor element, and before filling said insulating resinpaste, said opening is used to carry out an inspection of connectionbetween said semiconductor element and said circuit board.
 16. A methodfor manufacturing a semiconductor device according to claim 2, whereinsaid circuit board is a multi-layer printed circuit board.
 17. A methodfor manufacturing a semiconductor device according to claim 3, whereinsaid circuit board is a multi-layer printed circuit board.